Graphene is attracting a great deal of attention because of its excellent properties. With respect to graphene, professors Geim and Novoselov at the University of Manchester first succeeded in separating atomic layers from graphite using scotch tape in the year 2004 and were awarded the Nobel Prize for their discovery of graphene in the year 2010. In the year 2010, a roll-to-roll transfer technique of manufacturing large-area graphene having an area of 30 inches was reported, and technologies enabling graphene to be industrially applied have been continuously developed. For industrial application, graphene is required to be formed uniformly as a single layer. In the prior art, the use of general copper foils suffers from a problem in that multilayer graphene is present as islands or an epitaxial graphene layer or epitaxial graphene layers do not easily grow.
In the manufacturing of graphene electrodes, the surface energy state of a metal catalyst is important for the epitaxial growth of monolayer graphene. This is because the atomic packing density of a metal varies depending on the orientation of the metal and because factors, including dislocation density, stacking fault energy, twins and impurities, which influence the surface energy of the catalyst, influence the reaction with the gaseous molecules or atoms to be adsorbed. Particularly, when a metal has low solubility or low reactivity with the element to be adsorbed, it barely acts as a catalyst. For example, copper is frequently used for the formation of graphene thin films and has a face-centered cubic (FCC) structure. However, the solid solubility of carbon which is adsorbed onto the surface of the catalyst copper in CVD processes at 1000° C. is 0.028 at % or less. Due to this low reactivity, it is very difficult to control the adsorption of carbon atoms during the CVD processes. If structures having different orientations are present together, the energy state will become non-uniform, and thus the adsorption rate of carbon will differ between areas. This problem results in the growth of multilayer graphene in some areas to form graphite. Thus, to uniformly grow carbon on copper to form graphene thin films, it is effective to use as a catalyst a substrate which has a uniform energy state and at the same time, has formed thereon nucleation sites on which graphene nets are to be formed. Materials capable of satisfying a uniform energy state include single crystalline materials. Many studies thereon have been conducted, and particularly, studies on the use of single crystalline hexagonal FCC metals oriented in the (111) or (100) direction (for example, the study of Hori) or on single crystalline HCP metals having a (0001) plane have been conducted (J. Phys. Chem. B., Vol. 106, No. 1 15-17, 2002, Y. Hori et al.).
However, the results of the studies did not lead to industrialization, because only single crystalline metals having a size of several tens of nm can be prepared and it is impossible to obtain large areas which are industrially applicable. In addition, for industrial application, graphene is required to be formed uniformly as single layers, but the use of general copper foils in the prior art suffers from a problem in that multilayer graphene is present as islands, because the epitaxial growth rate of graphene is low.
The present inventors have developed a method for preparing a unidirectionally oriented metal catalyst for uniformly and epitaxially growing graphene and have found that the orientation and surface energy state of a catalyst substrate, particularly step structures, have a great influence on the adsorption of carbon atoms and the growth of graphene, thereby completing the present invention.